1. Field of the Invention
The present invention relates to an electrosurgical device having a control unit for controlling a high-frequency power output having a unique operational pattern.
2. Description of the Related Art
Electrosurgical devices such as a cautery knife is typically used to incise, coagulate, and blood stanch a body tissue in a surgical operation or a medical surgical operation. Such electrosurgical device includes a high-frequency cautery power supply and an instrument connected to the high-frequency cautery power supply. The electrosurgical device treats a body tissue of a patient with the high-frequency power supply applying the high-frequency power to the body tissue through the instrument which is in contact with the body tissue.
When the high-frequency power is applied onto the body tissue by the electrosurgical device, the body tissue is heated, and proteins thereof is denatured. The tissue is then dried with the moisture therewithin evaporated. In this process, the body tissue is coagulated. By continuously applying the high-frequency power to the body tissue even after the moisture contained therewithin is evaporated, the tissue is carbonized. The body tissue then begins to stick to the instrument. To prevent the body tissue from sticking to the instrument, the supply of the high-frequency power must be stopped when the body tissue starts being dried.
An electrosurgical device disclosed in Japanese Unexamined Patent Application Publication No. 8-98845 determines the end of coagulation referring to the tissue impedance of the body tissue and then stops the supply of the high-frequency power in order to prevent the body tissue from being carbonated and from sticking to an instrument.
To achieve the same object of Japanese Unexamined Patent Application Publication No. 8-98845, an electrosurgical device disclosed in Japanese Unexamined Patent Application Publication No. 10-225462 lowers a high-frequency output power.
In these conventional electrosurgical devices, the high-frequency power is applied to the body tissue as shown in FIG. 1A. The body tissue exposed to the high-frequency power is then heated as shown in FIG. 1B. The tissue temperature rapidly rises as the protein of the body tissue is denatured and the drying of the body tissue is in progress. Referring to FIG. 1C, the tissue impedance initially drops and then rapidly rises as the body tissue is dried.
The conventional electrosurgical device stops the supply of the high-frequency power at the moment the dried state is detected from the tissue impedance or the tissue temperature.
The conventional electrosurgical device outputs a rated power if the tissue impedance is in the vicinity of the rated value thereof. When the tissue impedance is deviated from the rated value thereof, the high-frequency power sharply drops in level. The electrosurgical device thus takes time to heat the body tissue to a desired temperature because of the drop of the high-frequency power.
When the body tissue to be coagulated is very large in size, the electrosurgical device must output the high-frequency power for a long period of time. This leads to an excessive temperature rise in the body tissue, thereby causing the body tissue to stick to the instrument.